The present invention relates to high-chi (χ) silicon-containing diblock copolymers for directed self-assembly (DSA) applications, and more specifically to high-chi (χ) silicon-containing diblock copolymers comprising a fluorinated surface-active linking group (junction group) joining the polymer blocks. Thin film layers of the diblock copolymers are capable of self-assembling to form perpendicularly oriented lamellae and/or cylindrical domain patterns.
In conventional lithography, ultraviolet (UV) radiation can be exposed through a mask onto a photoresist layer coated on a substrate or layered substrate. Positive or negative photoresists are useful and these can also contain a refractory element such as silicon to enable dry development with conventional integrated circuit (IC) plasma processing. In a positive photoresist, UV radiation transmitted through a mask causes a photochemical reaction in the photoresist, such that the exposed regions are removed by a developer solution or by conventional IC plasma processing. Conversely, in negative photoresists, UV radiation transmitted through a mask causes the regions exposed to radiation to become less removable by a developer solution or by conventional IC plasma processing. An integrated circuit feature, such as a gate, via or interconnect, is then etched into the substrate or layered substrate, and the remaining photoresist is removed. When using conventional lithographic exposure processes, the dimensions of features of the integrated circuit feature are limited. Further reduction in pattern dimensions are difficult to achieve with radiation exposure due to limitations related to aberrations, focus, proximity effects, minimum achievable exposure wavelengths and maximum achievable numerical apertures. Directed self-assembly is a promising approach that has been of interest in overcoming some of the drawbacks of conventional lithography as outlined above.
Specifically, directed self-assembly of block copolymers is a method useful for generating smaller patterned features for the manufacture of microelectronic devices in which the critical dimensions (CD) of features are typically on the nano-scale, so that feature sizes from 10 nm to 50 nm can be achieved. Achieving feature sizes below 10 nm using conventional approaches for directed self-assembly of block copolymers is challenging. Directed self-assembly methods such as those based on grapho-epitaxy and chemical epitaxy of block copolymers are desirable for extending the resolution capabilities of lithographic technology.
These techniques can be employed to either enhance conventional lithographic techniques by enabling the generation of patterns with higher resolution and/or improving CD control for EUV, e-beam, deep UV or immersion lithography. The block copolymers for directed self-assembly comprise an etch resistant polymer block and a selectively etchable polymer block, which when coated, aligned and etched on a substrate give regions of high resolution patterns.
Known examples of block copolymers for directed self-assembly are ones capable of microphase segregation and comprise a block rich in carbon (such as styrene) which is resistant to plasma etch, and a block which is highly plasma etchable or removable, which can provide a high resolution pattern definition. Examples of highly etchable blocks can comprise monomers that are rich in oxygen and which do not contain refractory elements, and are capable of forming blocks which are highly etchable, such as methyl methacrylate. The plasma etch gases used in the etching process of defining the self-assembly pattern typically are those used in processes to make integrated circuits (IC). In this manner fine patterns can be created on typical IC substrates compared to conventional lithographic techniques, thus achieving pattern multiplication. However, domain patterns formed by diblock copolymers having a half-pitch <10 nm are also prone to significant etch-induced degradation of the critical dimension uniformity of the domain (e.g., poly(styrene) domain) left by the etch, which is not observed for the same domain composition at higher pitches.
In the grapho-epitaxy directed self-assembly method, a substrate is pre-patterned using conventional lithography (Ultraviolet, Deep UV, and e-beam, Extreme UV (EUV) exposure source) to form topographical features such as a line/space (L/S) or contact hole (CH) pattern. A thin layer of block copolymer for self-assembly is then disposed on the pre-pattern. In an example of L/S directed self-assembly array, the block copolymer can form self-aligned lamellar regions with a sub-lithographic pitch in the trenches between sidewalls of pre-pattern, thus enhancing pattern resolution by subdividing the space in the trench between the topographical lines into finer patterns. Similarly, features such as contact holes can be made denser by using grapho-epitaxy, in which a suitable block copolymer arranges itself by directed self-assembly within an array of pre-patterned holes or pre-patterned posts defined by conventional lithography, thus forming a denser array of regions of etchable and etch resistant domains, which when etched give rise to a denser array of contact holes. In addition, block copolymers can form a single and smaller etchable domain at the center of pre-pattern hole with proper dimension and provide potential shrink and rectification of the hole in pre-pattern. Consequently, grapho-epitaxy has the potential to offer both pattern rectification and pattern multiplication.
In chemo-epitaxy DSA methods, the self-assembly of the block copolymer occurs on a surface that has regions of differing chemical affinity but no or very slight topography to guide the self-assembly process. For example, the chemical pre-pattern could be fabricated using lithography (UV, Deep UV, e-beam, EUV) and nanofabrication process to create surfaces of different chemical affinity in a line and space (L/S) pattern. These areas may present little to no topographical difference, but do present a surface chemical pattern to direct self-assembly of block copolymer domains. This technique allows precise placement of the block copolymer domains of higher spatial frequency than the spatial frequency of the pre-pattern. The aligned block copolymer domains can be subsequently pattern transferred into an underlying layer of the substrate after plasma or wet etch processing. In addition, chemo-epitaxy has the advantage that block copolymer self-assembly can rectify variations in the surface chemistry, dimensions, and roughness of the underlying chemical pattern to yield improved line-edge roughness and CD control in the final self-assembled block copolymer domain pattern. Other types of patterns such as contact holes (CH) arrays can also be generated or rectified using chemo-epitaxy.
The ability of a BCP to phase separate depends in part on the Flory Huggins interaction parameter (χ), written also as “chi” herein. PS-b-PMMA (poly(styrene-block-methyl methacrylate) has been studied extensively for directed self-assembly (DSA) applications. However, the minimum half-pitch of PS-b-PMMA is limited to about 10 nm because of the lower chi parameter between PS and PMMA. To enable further feature miniaturization, a block copolymer with a larger interaction parameter between two blocks (higher chi) is highly desirable.
For lithography applications, orientation of the block copolymer domains perpendicular to the substrate is desirable. For a conventional block copolymer such as PS-b-PMMA in which both blocks have similar surface energies at the BCP-air interface, this can be achieved by coating and thermally annealing the block copolymer on a layer of non-preferential or neutral material that is grafted or cross-linked at the polymer-substrate interface. Due to larger difference in the interaction parameter between the domains of higher-χ block copolymers, it is important to control both BCP-air and BCP-substrate interactions. Many orientation control strategies for generating perpendicularly oriented BCP domains have been implemented with higher-χ BCPs. For example, solvent vapor annealing has been used for orientation control of polystyrene-b-polyethylene oxide (PS-b-PEO), polystyrene-b-polydimethylsiloxane (PS-b-PDMS), polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP), polylactide-b-poly(trimethylsilylstyrene) PLA-b-PTMSS and PαMS-b-PHOST. Introducing a solvent vapor chamber and kinetics of solvent vapor annealing may complicate DSA processing. Alternatively, the combination of neutral underlayers and topcoat materials has been applied to PS-b-P2VP, PS-b-PTMSS and PLA-b-PTMSS to achieve perpendicular orientation of the polymer domains. However, the additional topcoat materials can increase the process cost and complexity.
There exists a need for a topcoat-free high-chi BCP having a half pitch less than 10 nm that self-assembles when thermally annealed, forming a perpendicularly oriented domain pattern on a range of preferential and non-preferential substrates. Additionally, there is a need for the domain pattern, when selectively etched, to produce a relief pattern of acceptable dimensional uniformity.